I'm with Wayne on 3F for large bores.

I tested my 14 bore ML with both 3F and 2F GOEX over the chronograph and 2f outperformed 3F as to velocity and accuracy.

If wanting even better regulation, one might try Swiss powder. I would think 1 1/2F would be about right, but 2F might do as well.

You may be able to reduce the load a bit, but know that the Swiss will develop about the same speeds, at the same pressure.

That means you might be able to drop from 90gr. to 75gr. or 80gr. and get the same regulation/velocities as GOEX, if switching to Swiss, and Swiss costs about 50% more.